# C++ Support in Clang

Last updated: $Date$

Clang fully implements all published ISO C++ standards (C++98 / C++03, C++11, and C++14), and most of the upcoming C++17 standard.

The Clang community is continually striving to improve C++ standards compliance between releases by submitting and tracking C++ Defect Reports and implementing resolutions as they become available.

Experimental work is also under way to implement C++ Technical Specifications that will help drive the future of the C++ programming language.

The LLVM bug tracker contains Clang C++ components that track known bugs with Clang's language conformance in each language mode.

## C++98 implementation status

Clang implements all of the ISO C++ 1998 standard (including the defects addressed in the ISO C++ 2003 standard) except for `export` (which was removed in C++11).

## C++11 implementation status

Clang 3.3 and later implement all of the ISO C++ 2011 standard.

By default, Clang builds C++ code according to the C++98 standard, with many C++11 features accepted as extensions. You can use Clang in C++11 mode with the `-std=c++11` option. Clang's C++11 mode can be used with libc++ or with gcc's libstdc++.

List of features and minimum Clang version with support

Language Feature | C++11 Proposal | Available in Clang?
--- | --- | ---
Rvalue references | N2118 | Clang 2.9
Rvalue references for `*this` | N2439 | Clang 2.9
Initialization of class objects by rvalues | N1610 | Clang 2.9
Non-static data member initializers | N2756 | Clang 3.0
Variadic templates | N2242 | Clang 2.9
Extending variadic template template parameters | N2555 | Clang 2.9
Initializer lists | N2672 | Clang 3.1
Static assertions | N1720 | Clang 2.9
`auto`-typed variables | N1984 | Clang 2.9
Multi-declarator `auto` | N1737 | Clang 2.9
Removal of auto as a storage-class specifier | N2546 | Clang 2.9
New function declarator syntax | N2541 | Clang 2.9
Lambda expressions | N2927 | Clang 3.1
Declared type of an expression | N2343 | Clang 2.9
Incomplete return types | N3276 | Clang 3.1
Right angle brackets | N1757 | Clang 2.9
Default template arguments for function templates | DR226 | Clang 2.9
Solving the SFINAE problem for expressions | DR339 | Clang 2.9
Alias templates | N2258 | Clang 3.0
Extern templates | N1987 | Clang 2.9
Null pointer constant | N2431 | Clang 3.0
Strongly-typed enums | N2347 | Clang 2.9
Forward declarations for enums | N2764 DR1206 | Clang 3.1
Standardized attribute syntax | N2761 | Clang 3.3 (1)
Generalized constant expressions | N2235 | Clang 3.1
Alignment support | N2341 | Clang 3.3
Conditionally-support behavior | N1627 | Clang 2.9
Changing undefined behavior into diagnosable errors | N1727 | Clang 2.9
Delegating constructors | N1986 | Clang 3.0
Inheriting constructors | N2540 | Clang 3.3
Explicit conversion operators | N2437 | Clang 3.0
New character types | N2249 | Clang 2.9
Unicode string literals | N2442 | Clang 3.0
Raw string literals | N2442 | Clang 3.0
Universal character names in literals | N2170 | Clang 3.1
User-defined literals | N2765 | Clang 3.1
Standard Layout Types | N2342 | Clang 3.0
Defaulted functions | N2346 | Clang 3.0
Deleted functions | N2346 | Clang 2.9
Extended friend declarations | N1791 | Clang 2.9
Extending `sizeof` | N2253 DR850 | Clang 3.1
Inline namespaces | N2535 | Clang 2.9
Unrestricted unions | N2544 | Clang 3.1
Local and unnamed types as template arguments | N2657 | Clang 2.9
Range-based for | N2930 | Clang 3.0
Explicit virtual overrides | N2928 N3206 N3272 | Clang 3.0
Minimal support for garbage collection and reachability-based leak detection | N2670 | N/A (2)
Allowing move constructors to throw [noexcept] | N3050 | Clang 3.0
Defining move special member functions | N3053 | Clang 3.0
Concurrency
Sequence points | N2239 | Clang 3.3
Atomic operations | N2427 | Clang 3.1
Strong Compare and Exchange | N2748 | Clang 3.1 (3)
Bidirectional Fences | N2752 | Clang 3.1
Memory model | N2429 | Clang 3.2
Data-dependency ordering: atomics and memory model | N2664 | Clang 3.2 (4)
Propagating exceptions | N2179 | Clang 2.9
Allow atomics use in signal handlers | N2547 | Clang 3.1
Thread-local storage | N2659 | Clang 3.3 (5)
Dynamic initialization and destruction with concurrency | N2660 | Clang 2.9
C99 Features in C++11
`__func__` predefined identifier | N2340 | Clang 2.9
C99 preprocessor | N1653 | Clang 2.9
`long long` | N1811 | Clang 2.9
Extended integral types | N1988 | N/A (6)

(1): The `[[carries_dependency]]` attribute has no effect.
(2): No compiler changes are required for an implementation such as Clang that does not provide garbage collection.
(3): All compare-exchange operations are emitted as strong compare-exchanges.
(4): `memory_order_consume` is lowered to `memory_order_acquire`.
(5): `thread_local` support requires a C++ runtime library providing `__cxa_thread_atexit`, such as libc++abi 3.6 or later, or libsupc++ 4.8 or later.
(6): No compiler changes are required for an implementation such as Clang that does not provide any extended integer types. `__int128` is not treated as an extended integer type, because changing `intmax_t` would be an ABI-incompatible change.

## C++14 implementation status

Clang 3.4 and later implement all of the ISO C++ 2014 standard.

You can use Clang in C++14 mode with the `-std=c++14` option (use `-std=c++1y` in Clang 3.4 and earlier).

List of features and minimum Clang version with support

Language Feature | C++14 Proposal | Available in Clang?
--- | --- | ---
Tweak to certain C++ contextual conversions | N3323 | Clang 3.4
Binary literals | N3472 | Clang 2.9
decltype(auto) | N3638 | Clang 3.3
Return type deduction for normal functions | Clang 3.4
Initialized lambda captures | N3648 | Clang 3.4
Generic lambdas | N3649 | Clang 3.4
Variable templates | N3651 | Clang 3.4
Relaxing requirements on constexpr functions | N3652 | Clang 3.4
Member initializers and aggregates | N3653 | Clang 3.3
Clarifying memory allocation | N3664 | Clang 3.4
`[[deprecated]]` attribute | N3760 | Clang 3.4
Single quotation mark as digit separator | N3781 | Clang 3.4
C++ Sized Deallocation | N3778 | Clang 3.4 (7)

(7): In Clang 3.7 and later, sized deallocation is only enabled if the user passes the `-fsized-deallocation` flag. The user must supply definitions of the sized deallocation functions, either by providing them explicitly or by using a C++ standard library that does. `libstdc++` added these functions in version 5.0, and `libc++` added them in version 3.7.

## C++17 implementation status

Clang SVN implements all the features of the C++ 2017 Draft International Standard.

You can use Clang in C++17 mode with the `-std=c++1z` option.

List of features and minimum Clang version with support

Language Feature | C++17 Proposal | Available in Clang?
--- | --- | ---
`static_assert` with no message | N3928 | Clang 3.5
Disabling trigraph expansion by default | N4086 | Clang 3.5
`typename` in a template template parameter | N4051 | Clang 3.5
New `auto` rules for direct-list-initialization | N3922 | Clang 3.8 (8)
Fold expressions | N4295 | Clang 3.6
P0036R0 | Clang 3.9
`u8` character literals | N4267 | Clang 3.6
Nested namespace definition | N4230 | Clang 3.6
Attributes for namespaces and enumerators | N4266 | Clang 3.6
Allow constant evaluation for all non-type template arguments | N4268 | Clang 3.6
Remove deprecated `register` storage class | P0001R1 | Clang 3.8
Remove deprecated `bool` increment | P0002R1 | Clang 3.8
Make exception specifications part of the type system | P0012R1 | Clang 4
`__has_include` in preprocessor conditionals | P0061R1 | Yes
New specification for inheriting constructors (DR1941 et al) | P0136R1 | Clang 3.9 (9)
`[[fallthrough]]` attribute | P0188R1 | Clang 3.9
`[[nodiscard]]` attribute | P0189R1 | Clang 3.9
`[[maybe_unused]]` attribute | P0212R1 | Clang 3.9
Aggregate initialization of classes with base classes | P0017R1 | Clang 3.9
`constexpr` lambda expressions | P0170R1 | SVN
Differing `begin` and `end` types in range-based `for` | P0184R0 | Clang 3.9
Lambda capture of `*this` | P0018R3 | Clang 3.9
Direct-list-initialization of `enum`s | P0138R2 | Clang 3.9
Hexadecimal floating-point literals | P0245R1 | Yes
Using attribute namespaces without repetition | P0028R4 | Clang 3.9
Dynamic memory allocation for over-aligned data | P0035R4 | Clang 4
Template argument deduction for class templates | P0091R3 | SVN
P0512R0
Non-type template parameters with `auto` type | P0127R2 | Clang 4
Guaranteed copy elision | P0135R1 | Clang 4
Stricter expression evaluation order | P0145R3 | Clang 4 (10)
P0400R0
Requirement to ignore unknown attributes | P0283R2 | Yes
`constexpr` if-statements | P0292R2 | Clang 3.9
Inline variables | P0386R2 | Clang 3.9
Structured bindings | P0217R3 | Clang 4
Separate variable and condition for `if` and `switch` | P0305R1 | Clang 3.9
Matching template template parameters to compatible arguments | P0522R0 | Partial (12)
Removing deprecated dynamic exception specifications | P0003R5 | Clang 4
Pack expansions in using-declarations | P0195R2 | Clang 4

(8): This is a backwards-incompatible change that is applied to all language versions that allow type deduction from `auto` (per the request of the C++ committee). In Clang 3.7, a warning is emitted for all cases that would change meaning.
(9): This is the resolution to a Defect Report, so is applied to all language versions supporting inheriting constructors.
(10): Under the MS ABI, function parameters are destroyed from left to right in the callee. As a result, function parameters in calls to `operator<<`, `operator>>`, `operator->*`, `operator&&`, `operator||`, and `operator,` functions using expression syntax are no longer guaranteed to be destroyed in reverse construction order in that ABI.
(12): Despite being the the resolution to a Defect Report, this feature is disabled by default in all language versions, and can be enabled explicitly with the flag `-frelaxed-template-template-args` in Clang 4. The change to the standard lacks a corresponding change for template partial ordering, resulting in ambiguity errors for reasonable and previously-valid code. This issue is expected to be rectified soon.

## C++2a implementation status

Clang does not yet support any of the proposed features of the C++ standard following C++17, provisionally named C++2a. Note that support for these features may change or be removed without notice, as the draft C++2a standard evolves.

List of features and minimum Clang version with support

Language Feature | C++2a Proposal | Available in Clang?
--- | --- | ---
Default member initializers for bit-fields | P0683R1 | No
`const&`-qualified pointers to members | P0704R1 | No
Allow lambda-capture `[=, this]` | P0409R2 | No
`__VA_OPT__` for preprocessor comma elision | P0306R4 | No
Designated initializers | P0329R4 | Partial (extension)
template-parameter-list for generic lambdas | P0428R2 | No
Initializer list constructors in class template argument deduction | P0702R1 | No
Concepts | P0734R0 | No

## Technical specifications and standing documents

ISO C++ also publishes a number of documents describing additional language and library features that are not part of standard C++.

List of features and minimum Clang version with support

Document | Latest draft | Compiler flag | Available in Clang?
--- | --- | --- | ---
SD-6: SG10 feature test recommendations | SD-6 | N/A | Clang 3.4 (N3745)
Clang 3.6 (N4200)
Clang 4 (P0096R3)
Clang 5 (P0096R4)
[TS] Concepts | P0121R0 |  | WIP
[DRAFT TS] Coroutines | N4663 | `-fcoroutines-ts -stdlib=libc++` | SVN
[TS] Library Fundamentals, Version 1 (invocation type traits) | N4480 | N/A | No
[DRAFT TS] Library Fundamentals, Version 2 (`source_location`) | N4600 | N/A | No
[DRAFT TS] Modules | N4667 | `-fmodules-ts` | WIP
[TS] Transactional Memory | N4514 |  | No